1. Field of the Invention
This invention relates to photographic wide angle zoom lenses of the two-group type.
2. Description of the Prior Art
In general, photographic zoom lens can be varied from a wide angle region to a semi-telephoto region, and often the measure of increasing the number of constituent lens elements is taken, to achieve improvements in optical performance. The increase of the lens element number generally leads to the possibility of improving optical performance, but the complexity of the lens system is increased as a whole with the increase in the size. This results in disadvantages. The handling becomes inconvenient and the lens unit cost goes up.
To avoid an increase in the bulk and size of a zoom lens, it is the most effective to reduce the number of lens elements in each of the groups constituting the zoom lens. Particularly the 1st lens group counting from the front in most cases has the largest diameter, which is most responsible for the increase in the bulk and size of the zoom lens. Therefore, it has been the common practice to reduce the number of lens elements in the first group and to simplify the lens configuration so that a minimization of the bulk and size of the complete zoom lens is facilitated, as disclosed in, for example, Japanese Laid Open Patents Sho 53-60246 and Sho 54-114236. Any of these conventional lenses is, however, made to cover a relatively narrow angular field, and can be hardly said to belong to the category of zoom lenses of a range including the wide angle region.
It is also known to construct the first lens group from three lens elements as disclosed in U.S. Pat. No. 4,155,629 and from four lens elements with the use of an aspherical surface as disclosed in U.S. Pat. No. 4,159,865.